Dutch Language still Difficult for Automatic Translation
by Henk Nieland
English is a relatively easy language to automate. However, several
other languages, including Dutch and Latin, contain features which make
this far more difficult. At CWI a way has been found how to deal with some
of these difficulties by applying techniques used in mathematically defined
languages to the description of natural languages. The research is part
of a project in which the cross-fertilization of linguistics and computer
science is exploited.
"Vot flites aagh zair fghom Boston to Lozz Endzjelease tomogho
eefning?" CWI researcher Annius Groenink asked this question to a
large SUN workstation while visiting a colleague in Cambridge some time
ago. On the workstation ran a program that could translate spoken sentences
related to flight reservations into French. Ten seconds later it sounded
in good French: "Quels vols y a't-il de Boston a Los Angeles demain
soir?" The same sentence pronounced with a lot of ... euh ... 's in
it and with an even stronger Dutch-French accent did not lead the computer
astray. The colleague explained that only a real Frenchman can speak with
such an accent that the computer will go mad ... .
The example indicates how well translation jobs like this are handled
nowadays. For specific programmes with a restricted vocabulary, like flight
reservations, this is far better than is usually thought. However, automatic
translation still shows some substantial gaps that have not always sufficiently
drawn the technicians' attention. One of the reasons is their concentration
on English, which in a mysterious way is more related to computer languages
than Dutch. The difficulties in Dutch (for example the word order) present
themselves even stronger in Latin: "For the computer Latin is an extreme
form of Dutch", says Groenink.
Groenink first studied the necessary changes in existing description
techniques for natural languages in order to deal with more "complex"
languages like Dutch. To fit a language for automation its grammar should
be described with such precision that on this basis a computer can automatically
parse sentences. Such descriptions are being made nowadays with some regularity
for English and French, with satisfactory results.
However, existing methods turn out to have a rather poor performance
when applied to Dutch. One cause lies in the difficulties with the construction
of an underlying "tree structure" in Dutch. Contrary to English
and computer languages, many Dutch sentences do not have such a tree structure
(see Figure) - a well-known and old problem in linguistics.
The solution proposed by Groenink was known already for some time among
formal language theory researchers (strangely enough outside The Netherlands),
but was never applied in this context. A part of a sentence, which corresponds
to a branching point in the tree, is viewed not as just one string of words
within the sentence, but as two or more separate parts. Such extensions
of the existing methods provide in principle a description of Dutch which
can serve as a basis for automation. The proposed method turns out to work
also for a language like Latin, in which - according to common opinion
- the word order is completely free. Groenink formally showed that this
order is not at all as free as was assumed, thus giving latinists who doubted
this already, an argument to reinforce their ideas about the role of word
order in various kinds of Latin texts.
Word order also afflicts German, as can be seen in a translation program
of dictionary producer Langenscheidt (on the Web: http://www.gmsmuc.de/
trans.html). Simple German sentences are translated fairly well into
English or Spanish, but already a slight increase in complexity causes
the program to produce a totally wrong word order, and a sentence like
"Sah ich dich dem Mann gestern schwimmen helfen?" is not understood
at all.
To come up with a theoretical solution is one thing, to show that it
also works in practice is quite another story. Groenink paid particular
attention to the links between these two aspects of his research and proved
that his proposed extensions with regard to parsing do not cause an exponential
growth in computing time. In addition, Groenink could make plausible that
more realistic implementations of his software, where for example checks
on cases and singular/plural are included, also remain efficient. For more
information, see Annius Groenink's home page at http://www.cwi.nl/~avg/
Please contact:
Annius Groenink - CWI
Tel: +31 20 592 4113
E-mail: Annius.Groenink@cwi.nl
